Cumulative yield generally was as ex- 

 pected, with trees on M.26 EMLA producing 

 the most fruit and those on M.27 EMLA the 

 least. Pioneer Mac produced significantly more 

 fruit than Chic-A-Dee or Rogers, and Marshall 

 was intermediate; however, the relative 

 differences among the rootstocks varied with 

 cultivar. Cumulative yield of M.7 EMLA and 

 M.26 EMLA were similar for Pioneer Mac, 

 Chic-A-Dee, and Rogers, but Marshall/M.26 

 EMLA yielded more than double Marshall/M.7 

 EMLA (Figure 2). Rootstock effects on yield 

 efficiency followed consistent trends among 

 cultivars. Cumulatively, M.27 and Mark 

 produced the most efficient trees, followed by 

 M.26 EMLA, and M.7 EMLA produced the least 

 efficient trees (Table 2). Cumulatively, Pioneer 

 Mac and Chic-A-Dee were significantly more 



efficient than Marshall, with Rogers interme- 

 diate (Table 2). 



Rootstock did not affect fruit weight in 

 1997, but Chic-A-Dee resulted in significantly 

 larger fruit than Marshall or Pioneer Mac 

 (Table 2). 



Tliese results lead to an interesting 

 question: Why does Marshall Mcintosh 

 respond poorly to M.7 EMLA? One possibility 

 is that M.7 EMLA is sensitive to a virus present 

 in Marshall. Marshall is not a virus-fruit 

 strain of Mcintosh. It may explain some of the 

 variable results with Marshall Mcintosh in 

 recent years, particularly reduced leaf quality, 

 tree growth, and fruit size. If considering 

 semi dwarf Mcintosh trees for future plantings, 

 likely it is best to avoid the combination of 

 Marshall and M.7 EMLA. 



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Fruit Notes, Volume 62 (Number 4), Fall, 1997 



17 



